This invention relates to apparatus for the preparation of standard gas mixtures.
In my RSA Patent 90/8032, U.S. Pat. No. 5,147,612, is a description of apparatus for preparing accurate standard mixtures particularly for calibration of gas chromatographs (GCs), the apparatus comprising a closed cylinder, a piston sealingly movable in the cylinder and which defines a first and second chamber, piston rods of exactly the same diameter on either side of the piston and extending sealingly through the end walls of the cylinder, the piston having a valved passage therethrough so that gas may be moved from one chamber to the other by moving the piston a calculated distance corresponding to the volume of gas required to be moved, and means for introducing or withdrawing gas from either chamber.
Although that apparatus has been found to be very useful for most gas mixture ratios, the large surface area of the piston requires that, for the preparation of very dilute gas mixtures, the tiny movement required for the piston is difficult to control and measure accurately.
It is an object of the present invention to provide an apparatus which is not only of simpler construction than that of the previous invention but which also allows minute volumes of gas to be moved from one chamber to the other, i.e. It is capable of making accurately measurable mixtures down to vanishingly small concentrations.